The roller-lock delayed blowback action system has been employed in rifles and sub-machine guns since the 1950's and is well known to those familiar with firearm design, but it has not previously been employed in a semi-automatic shotgun. This is likely because the large diameter of the cartridge would require a disproportionately bulky mechanism and would interfere with the space necessary for feeding and ejecting the cartridges when situated near the front of the bolt—as in all previous known designs. However, it is desirable to provide a roller-lock delayed blowback action system for a shotgun because it would offer an alternative to: gas-operated systems that are subject to fouling; recoil-operated systems that are notoriously unreliable; and straight blowback systems that require an undesirable heavy bolt.
Additionally, a firearm incorporating known delayed-blowback roller-lock action system generally uses the same size or type of ammunition. As such, utilizing a constant resistance to impede rearward movement of the bolt and/or bolt carrier works well. In contrast, employing a constant or fixed amount of rearward resistance for use in a shotgun that is capable of firing a wide range of ammunition sizes and types—e.g., 2¾ inch light target loads, 3 inch magnum slug loads, non-lethal projectiles—does not work as well. Thus, to accommodate the wide range of ammunition utilized in a semi-automatic shotgun, there is a need for a delayed roller-lock action system capable of providing a variable amount of resistance to rearward movement of the bolt and/or bolt carrier.
The present invention is provided to address these and other considerations.